The piranhas of Rubi-Ka are largely unchanged descendants
of the ancient Earth genus. On Earth, these fish were
renowned for both their ferocity and their tenacity.
There were documented cases of a school of piranhas
devouring a cow in a few minutes, and also documented
cases of attacks on humans. Despite the danger, piranhas
became objects of interest, and sometimes were kept
as pets. It is believed that this is how the piranha
made it's way into Rubi-Ka's freshwater areas largely
unchanged from its original Earth-based descendant.

Recently, as Omni-Tek attempted to upgrade its weather
control system, the process had some undesired environmental
effects. These effects included the assumed total extinction
of the Piranhas and the Sharks.